Induction system for watercraft engine

ABSTRACT

An induction system employed in an engine of a small watercraft includes the first intake chamber communicating with the combustion chambers within the engine and a second intake chamber communicating with the first intake chamber. At least one auxiliary air aperture is provided in the first intake chamber so as to allow an auxiliary flow of air into the first intake chamber during, for example, sudden acceleration.

PRIORITY INFORMATION

[0001] This application is based on and claims priority to JapanesePatent Application No. 10-351851, filed Dec. 10, 1998, the entirecontents of which is hereby expressly incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention is directed to a watercraft, and moreparticularly to an improved air induction system employed in an engineof a watercraft.

[0004] 2. Description of the Related Art

[0005] Personal watercraft have become increasingly popular in recentyears. This type of watercraft is sporting in nature; it turns swiftly,it is easily maneuverable, and accelerates quickly. A personalwatercraft today commonly carries one rider and up to three passengers.Typically, the rider and passengers sit on a straddle-type seat that isformed by the hull of the watercraft. The straddle-type seat isgenerally aligned with the longitudinal axis of the hull.

[0006] The space beneath the straddle-type seat is usually used as anengine compartment for supporting and housing the engine within thewatercraft. The engine is preferably arranged within the enginecompartment so that the crankshaft of the engine is aligned with thelongitudinal axis of the watercraft. With the engine arranged as such,the crankshaft of the engine may be directly connected to an outputshaft for driving a propulsion unit. Additionally, such an arrangementallows the engine to be arranged at least partially within the seatpedestal. Arranged as such, the engine and the seat pedestal form acompact unit. During operation, the rider and any passengers straddlethe seat, and thus a portion of the engine while they are seated on thestraddle-type seat. This hull shape requires the engine to be in closespacing with the passengers during operation, thus allowing the overallsize of the watercraft to remain small, resulting in a compact andhighly maneuverable watercraft.

[0007] Although these watercraft are generally highly maneuverable andare used in a sporting manner, there is an interest in reducing thenoise generated by this type of watercraft. One part of the watercraftpropulsion system that can generate noise is the induction system of theengine. For the most part, the induction systems used for this type ofwatercraft have been designed primarily to ensure adequate air inductionand at least some filtration of the inducted air. Less effort has beengiven, however, to the silencing of the induction system.

[0008] In response to the noise generated by two-cycle engines, whichare commonly employed in personal watercraft, certain recreationalfacilities have banned the operation of two-cycle engine poweredwatercraft. Such bans have resulted in a decrease in popularity ofpersonal watercraft powered by two-cycle engines.

[0009] Obviously, it is necessary for the induction system to be able toingest an adequate flow of air for maximum engine performance. In manyinstances, the induction systems previously proposed for watercraft havenot recognized the advantages of using a tuning arrangement on theintake side of the engine. One reason for this is that the spaceavailable in an engine compartment of a personal watercraft generallydoes not afford room for various types of intake tuning systems.Although it has been known that a large intake air box will prevent thegeneration of loud noises in the induction system and will generate asmooth flow of air into the combustion chambers, the small spaceavailable in the hulls of small watercraft have prevented the use oflarge air boxes. In addition, the space available makes it difficult totune the induction system to improve intake efficiency.

[0010] For example, a large air box mounted so as to feed the intakerunners arranged along one side of an engine within the enginecompartment of a watercraft will tend to attenuate induction noises andimprove intake efficiency. However, as discussed above, engines arepreferably arranged within the seat pedestals of personal watercraftsuch that their crankshaft is aligned with the longitudinal axis of thewatercraft. As such, the intake runners open at a side of the enginebody, facing an inner wall of the seat pedestal. Therefore, the size ofthe intake air box affects the overall width of the engine. If a largeintake air box is used, the overall width of the engine is increased.

[0011] Since the rider and any passengers straddle the seat pedestal andengine during operation, the overall width of the engine is limited tothat which would fit within a straddle-type seat pedestal. If thepedestal is too wide, a rider cannot comfortably sit on the seatpedestal during operation of the watercraft. Therefore, any portions ofthe engine mounted along either side of the engine body, such as theinduction system, should be small enough such that the engine can stillfit within the seat pedestal defining an engine compartment of thewatercraft.

[0012] Additionally, because of its sporting nature, personal watercraftare oftentimes laid on their side or are flipped over by advanced ridersduring use. It thus is also important that the induction system bedesigned in such a way to inhibit ingesting water, which may be presentin the engine compartment, into the engine through the induction system.

SUMMARY OF THE INVENTION

[0013] A need therefore exists for a compact induction system employedin an engine of a watercraft which reduces noise and which allows asufficient flow of combustion air to enter the induction system underall operating conditions. For example, it is desirable to provide aninduction system for a watercraft engine which allows for asubstantially instantaneous increase in air flow during a suddenmovement of the throttle from an idle to a fully open position.

[0014] According to one aspect of the present invention, an inductionsystem employed in an engine of a small watercraft includes a firstintake air chamber communicating with at least one combustion chamber ofthe engine, and a second intake air chamber communicating with the firstintake air chamber. The first intake air chamber includes a plurality ofwalls defining an interior volume within the first intake air chamber.According to the present aspect of the invention, the first intake airchamber includes at least one auxiliary air aperture formed in one ofthe walls defining the interior volume. By providing the first intakeair chamber with at least one auxiliary air aperture, the presentinvention allows an auxiliary flow of air to flow into the first intakeair chamber after a sudden opening of the throttle, while benefitingfrom the quieting and smoothing effects provided by the inclusion offirst and second intake air chambers.

[0015] One aspect of the present invention includes the realization thatcertain induction systems are slow to respond to sudden increases in theair flow rate required by the engine. For example, when an engine of asmall watercraft is idling, and the throttle is suddenly moved to awide-open position, the air flow rate needed to produce the maximumpower output from the engine also rises suddenly. However, it has beenfound that induction systems that have noise attenuatingcharacteristics, generate at least some friction and/or air resistancewhich causes a delay in the acceleration of the air flow therethrough.For example, an induction system which includes two intake chamberscommunicating with one another so as to form an induction air flow path,attenuates induction noise and smoothes the flow of air therethrough.However, such an induction system also generates at least some frictionand thus a delay in air flow acceleration. It has been found that such adelay causes a corresponding delay in the power output of the engine,thereby slowing the acceleration of the watercraft.

[0016] By providing the first intake air chamber with a auxiliary airaperture, the induction system of the present invention allows anauxiliary flow of air to enter the first intake air chamber while themain flow of air entering the first intake air chamber from the secondintake air chamber accelerates. By allowing the auxiliary flow of air toenter the first intake air chamber, the present invention provides theengine with a sufficient air flow to feed the engine when the throttleis suddenly moved to a wide open position. Therefore, the presentinvention enhances the performance of a watercraft engine whileremaining quiet, and smoothing the air flow into the engine.

[0017] In a preferred embodiment, the auxiliary air aperture is formedon an inner wall of the first intake air chamber which is positionedbetween the interior of the first intake air chamber and the engine. Byarranging the auxiliary air aperture as such, the likelihood that watermay splash into the auxiliary air aperture is greatly reduced.

[0018] Further aspects, features, and advantages of the presentinvention will become apparent from the Detailed Description of thePreferred Embodiment which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above-mentioned and other features of the invention will nowbe described with reference to the drawings of a preferred embodiment ofthe present induction system. The illustrated embodiment is intended toillustrate, but not to limit the invention. The drawings contain thefollowing figures:

[0020]FIG. 1 is a partial cut-away side elevational view of a watercrafthaving an induction system constructed in accordance with the presentinvention, with some internal components of the watercraft shown inphantom lines;

[0021]FIG. 2 is a top plan view of the watercraft shown in FIG. 1, withthe internal components shown in phantom lines;

[0022]FIG. 3 is a left side elevational view of an engine having aninduction system constructed in accordance with the present invention;

[0023]FIG. 4 is a front elevational view of the engine shown in FIG. 3;

[0024]FIG. 5 is a top plan view of the engine shown in FIG. 4, withcharge formers shown in phantom;

[0025]FIG. 6 is a rear elevational view of the engine shown in FIG. 5,with a rear of an exhaust system removed;

[0026]FIG. 7 is a partial cut-away view of an intake air chamberconstructed in accordance with one aspect of the present invention, withan outer cover removed;

[0027]FIG. 8 is a partial cross-sectional and enlarged view of theintake air chamber shown in FIG. 6, mounted to a charge former;

[0028]FIG. 9 is a front elevational view of an inner wall of the intakeair chamber shown in FIG. 7;

[0029]FIG. 10 is a side elevational view of the outer cover shown inFIG. 9;

[0030]FIG. 11 is a cross-sectional view taken along line 11-11 of theinner wall shown in FIG. 9;

[0031]FIG. 12 a cross-sectional view taken along line 12-12 of the innerwall shown in FIG. 9;

[0032]FIG. 13 is a rear elevational view of the inner wall shown in FIG.8;

[0033]FIG. 14 is a bottom plan view of the inner wall shown in FIG. 13;

[0034]FIG. 15 is an elevational view of an inner portion of the outercover of the intake air chamber shown in FIG. 8;

[0035]FIG. 16 is a top plan view of the outer cover shown in FIG. 15;

[0036]FIG. 17 is a side elevational view of the outer cover shown inFIG. 15;

[0037]FIG. 18 is a cross-sectional view taken along line 18-18 shown inFIG. 15;

[0038]FIG. 19 is an enlarged partial elevational view of a sealinggroove between the outer cover and the inner wall of an air box inaccordance with the preferred embodiment of the present invention;

[0039]FIG. 20 is a cross-sectional view of a sealing member for use inthe sealing groove shown in FIG. 19; and

[0040]FIG. 21 is a cross-sectional view of the sealing member shown inFIG. 20 mounted in a sealing groove shown in FIG. 19.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0041]FIGS. 1 and 2 illustrate different views of a small watercraftincorporating an induction system configured in accordance with thepreferred embodiment of the present invention. The induction systemincludes enhanced airflow characteristics, which enhances engineperformance particularly during sudden acceleration.

[0042]FIG. 1 illustrates a personal watercraft 10 which includes aninduction system 12 configured in accordance with the preferredembodiment of the present invention. Although the present inductionsystem 12 is illustrated in connection with a personal watercraft, theillustrated induction system 12 can be used with other types ofwatercraft as well, such as, for example, but without limitation, smalljet boats and the like. Before describing the induction system 12, anexemplary personal watercraft 10 will first be described in generaldetails to assist the reader's understanding of the environment of useand the operation of the induction system 12.

[0043] The watercraft 10 includes a hull 14 formed by a lower hullsection 16 and an upper deck section 18. The hull sections 16, 18 areformed from a suitable material, such as, for example, a moldedfiberglass reinforced resin (e.g., SMC). The lower hull section 16 andthe upper deck section 18 are fixed to each other around a peripheraledge 20 in any suitable manner.

[0044] As viewed in the direction from the bow to the stem of thewatercraft, the upper deck section 18 includes a bow portion 20, acontrol mast 22, and a rider's area 24. The bow portion 20 slopesupwardly toward the control mast 22 and includes at least one air duct26 through which air can enter the hull 14. A hatch cover 28 desirablyextends above an upper end of the air duct 26 to inhibit an influx ofwater into the hull.

[0045] The hatch cover 28 is preferably attached to the upper decksection 18 via a hinge. The hatch cover 28 provides access to an accesshole which may be used to provide access to a storage compartment forstoring any other desired item.

[0046] A fuel tank 30 is preferably located within the hull 14 beneaththe hatch cover 28. Conventional means, such as, for example, straps,are preferably used to secure the fuel tank 30 to the lower hull section16.

[0047] The control mast 22 extends upward from the bow portion 20 andsupports a handlebar assembly 32. The handlebar 32 controls the steeringof the watercraft 10 in a conventional manner. The handlebar assembly 32also carries a variety of controls of the watercraft 10, such as, forexample, a throttle control, a start switch and a lanyard switch.

[0048] A display panel (not shown) is desirably located in front of thecontrol mast 22 on the bow portion 20 and is oriented to be visible bythe rider. The display panel desirably displays a number of performancecharacteristics of the watercraft, such as, for example, watercraftspeed (via a speedometer), engine speed (via a tachometer), fuel level,oil level, engine temperature, battery charge level, and the like.

[0049] The rider's area 24 lies behind the control mast 22 and includesa seat assembly 34. In the illustrated embodiment, the seat assembly 34has a longitudinally extending straddle-type shape that may be straddledby an operator and by at least one to three passengers. The seatassembly 34, at least in principal part, is formed by a seat cushion 36supported by a raised pedestal 38.

[0050] The raised pedestal 38 has an elongated shape and extendslongitudinally along the center of the watercraft 10. The seat cushion36 desirably is removably attached to a top surface of the pedestal 38and covers the entire upper end of the pedestal for rider and passengercomfort.

[0051] As shown in FIG. 6, an access opening 40 is preferably located onan upper surface of the pedestal 38. The access opening 40 opens into anengine compartment 42 formed within the hull 14. The seat cushion 36normally covers and seals the access opening 40. When the seat cushion36 is removed, the engine compartment 42 is accessible through theaccess opening 40.

[0052] As shown in FIG. 1, the pedestal 38 also desirably includes atleast one air duct 44 located behind the access opening 40. The air duct44 communicates with the atmosphere through a space formed between thepedestal 38 and the seat cushion 36, which is formed behind the accessopening 40. Air can pass through the rear duct 44 in both directions.

[0053] As shown in FIG. 2, the upper deck section 18 advantageouslyincludes a pair of raised gunnels 46 positioned on opposite sides of theaft end of the upper deck 18. The raised gunnels 46 define a pair offoot areas 48 that extend generally longitudinally and parallel to thesides of the pedestal 38. In this position, the operator and anypassengers sitting on the seat assembly 34 can place their feet in thefoot areas 48 with the raised gunnels 46 shielding the feet and lowerlegs of the riders. A non-slip (e.g., rubber) mat desirably covers thefoot areas 48 to provide increased grip and traction for the operatorand the passengers. The lower hull portion 16 principally defines theengine compartment 42. Except for the air ducts, the engine compartment42 is normally substantially sealed so as to enclose an engine 50 of thewatercraft 10 from the body of water in which the watercraft isoperated.

[0054] The lower hull section 16 is designed such that the watercraft 10planes or rides on a minimum surface area at the aft end of the lowerhull 16 in order to optimize the speed and handling of the watercraft 10when up on plane. For this purpose, the lower hull section 16 generallyhas a V-shaped configuration formed by a pair of inclined sections thatextend outwardly from a keel line of the hull to the hull's side wallsat a dead rise angle. The inclined sections also extend longitudinallyfrom the bow toward the transom of the lower hull section 16. The sidewalls are generally flat and straight near the stem of the lower hull 16and smoothly blend towards the longitudinal center of the watercraft atthe bow. The lines of intersection between the inclined sections and thecorresponding side walls form the outer chines of the lower hullsection.

[0055] As shown in FIG. 2, toward the transom of the watercraft, arecessed channel or tunnel 52 is formed on the lower surface of thelower hull section 16. The watercraft 10 includes a jet pump unit 54which produces a rearwardly directed flow of water which generates apropulsion force to thereby cause forward and/or reverse movement of thewatercraft 10.

[0056] The jet pump unit 54 is mounted within the tunnel 52 by aplurality of bolts. An intake duct of the jet pump unit 54 defines aninlet opening (not shown) that opens into a gullet. The gullet leads toan impeller housing assembly in which the impeller of the jet pump unit54 operates. An impeller housing assembly also acts as a pressurizationchamber and delivers the water flow from the impeller housing to adischarge nozzle housing.

[0057] The jet pump unit 54 desirably includes a steering nozzle at itsaft end. The steering nozzle is connected to the handlebar assembly 32through, for example, a bowden-wire actuator, as known in the art. Inthis manner, the operator of the watercraft 10 could move the steeringnozzle to effect directional changes of the watercraft 10.

[0058] A ride plate (not shown) preferably covers a portion of thetunnel 52 behind the inlet to enclose the jet pump assembly 54 and anozzle assembly thereof. The aft end of an impeller shaft (not shown) issuitably supported and journaled within the engine chamber 42 of theassembly in a known manner. The impeller shaft extends in a forwarddirection through a front wall of the tunnel 52 and/or a bulkhead (notshown).

[0059] With reference to FIG. 1, the internal combustion engine 50 ofthe watercraft 10 powers the impeller shaft to drive the impeller of thejet pump unit 54. The engine 50 is positioned within the enginecompartment 42 and is mounted primarily beneath the riders' area 24. Aplurality of vibration absorbing engine mounts 56, as shown in FIG. 6,are preferably used to secure the engine 50 to the lower hull portion 16in a known manner. The engine 50 is mounted in approximately a centralposition within the watercraft 10.

[0060] With reference to FIG. 6, the engine 50 includes three in-linecylinders and operates on a two-stroke, crankcase compression principal.The engine 50 is positioned such that the row of cylinders lies parallelto the longitudinal axis of the watercraft 10, running from bow to stem.The cylinders are formed within a cylinder block 51, which is mounted toa crank case 53 at a lower end, and a cylinder head 55 at an upper end,as shown in FIG. 6. The cylinder block 51 defines three cylinders 51 a,51 b, and 51 c, as shown in FIG. 7. The axis of each cylinder 51 a, 51b, 51 c may be parallel, skewed, or inclined, relative to the verticalcentral plane of the watercraft 10, in which the longitudinal axis lies.This engine type, however, is merely exemplary. Those skilled in the artwill readily appreciate that the present induction system can be usedwith any of a variety of engine types having other numbers of cylinders,having other cylinder arrangements and operating on other combustionprincipals (e.g., four stroke and rotary principles).

[0061] With reference to FIG. 2, the jet pump unit 54 preferablysupplies cooling water through a conduit (not shown) to an enginecooling jacket (not shown). For this purpose, an outlet port may beformed on the housing of the jet pump unit 54. The conduit may becoupled to an outlet port and extends to an inlet port for supplyingcoolant, such as water, to the engine cooling jacket. The engine coolingjacket extends through the exhaust manifold, the cylinder block, aboutthe cylinders, and through the cylinder head assembly. The cylinder headassembly and/or the exhaust manifold can include a coolant dischargeport through which the cooling water exits the engine and flows throughat least a portion of an exhaust system 58.

[0062] With reference to FIGS. 1 and 2, the exhaust system 58 of theengine is generally comprised of an exhaust pipe 59 which connects thecombustion chambers defined within the cylinder block 51 to theatmosphere. The exhaust passage comprises an exhaust manifold 60 mountedto the side of the engine 50 so as to communicate with the combustionchambers defined within the engine 50. The exhaust manifold 60, at adischarge end, is connected to an exhaust passage 62, which is connectedto an expansion chamber 64. As shown in FIG. 5, a downstream end 66 ofthe expansion chamber 64 communicates with the catalytic device chamber68 through a coupling 70. As shown in FIG. 3, the catalytic devicechamber 68 preferably includes a catalytic device 72 formed of acatalytic bed.

[0063] The exhaust manifold 60, the exhaust passage 62, the expansionchamber 64, the downstream end 66, and the catalytic device chamber 68each include a coolant jacket in thermal communication therewith. Thecoupling 70 preferably comprises an exhaust passage directed through acenter thereof and a coaxial coolant passage which connects the coolingjacket formed around the downstream end 66 to the cooling jacket formedaround catalytic device chamber 68.

[0064] With reference to FIG. 1, downstream from the catalytic devicechamber 68, the exhaust system 58 includes a downturned portion 74 whichleads to a water trap device 76. As shown in FIGS. 1 and 3, thedownturned portion 74 is connected to the water trap device 76 via acoupling 78, which may comprise a flexible pipe. The water trap device76 includes an outlet 80 leading to a discharge pipe 82 that terminatesin an exhaust discharge 84.

[0065] The exhaust discharge 84 is desirably positioned so as toterminate in the hull tunnel 52. Preferably, the exhaust discharge 84 ispositioned above or below the water line of the watercraft 10.

[0066] With reference to FIGS. 3 and 5, the expansion chamber 64 of theexhaust system 58 is preferably supported by one or more mountingbracket(s) 86. The expansion chamber 64 is connected to the mountingbracket 86 by a plurality of bolts, to support the forward portion ofthe exhaust system 58. Additionally, as shown in FIGS. 3, 4, and 6, thecatalytic device chamber 68 and at least a portion of the downturnedportion 74 have a heat shield 88 mounted thereon. The heat shield 88 ismade from a suitably heat resistant material, such as resin, or othermaterials appropriate for use as a heat shield.

[0067] In operation, exhaust gases are discharged from the combustionchambers within the engine 50 to the exhaust manifold 60. The exhaustgases then flow out of the exhaust manifold 60 and through the exhaustpassage 62, expansion chamber 64, catalytic device 72, downturnedportion 74, water trap device 76, discharge pipe 82, and discharge 84.During operation, as discussed above, the exhaust manifold 60, theexhaust passage 62, the expansion chamber 64, the catalytic devicechamber 68, and at least a portion of the downturn portioned 74, arecooled by a flow of water produced by the jet pump unit 54, and directedinto the respective coolant jackets in thermal communication therewith.

[0068] The personal watercraft 10 so far described represents only anexemplary watercraft on which the present induction system 12 can beemployed. A further description of the personal watercraft 10 is notbelieved to be necessary for an understanding and an appreciation of thepresent induction system 12. The induction system 12 will now bedescribed in detail.

[0069] With reference to FIGS. 4 and 5, the induction system 12 includesa first intake air chamber 90. The first intake air chamber 90 ispreferably formed of an inner wall member 94 connected to intake runners96, and a cover member 98 engaged with the wall member 94 along ajoining portion 100 formed therebetween, so as to define an interiorvolume 101. A detailed description of the first intake air chamber 90 isset forth below with reference to FIGS. 7-21.

[0070] As shown in FIG. 5, the intake runners 96 communicate with fuelcharge formers 102. Together, the intake runners 96 and fuel chargeformers 102 deliver a fuel and air mixture to the crankcase 104 of theengine 50 for combustion within the combustion chambers 106 which areschematically represented in FIG. 5. In the illustrated embodiment,floatless-type carburetors act as the fuel charge formers 102, andcommunicate with individual crankcase chambers through intake pipes 97.Fuel injectors can also be used as the charge formers, and can bearranged either for direction injection or for intake injection (i.e.,communicate with the intake pipes 97). In either case, the intake pipes97 would extend from the first intake chamber 92 to the individualcrankcase chambers. Alternatively, the engine 50 could be constructed tooperate under a direct injection principle, under which, the fuel chargeformers 102 would be mounted to the cylinder head 55.

[0071] As discussed above, in the illustrated embodiment, the engine 50operates under a crankcase compression principal. However, it is readilyunderstood by one of ordinary skill in the art that the induction system12 can be used with other types of engines operating on other principalsof operation, such as four stroke and rotary principals.

[0072] With reference to FIG. 5, the first intake air chamber 90includes an inlet 104 which communicates with a second intake airchamber 106 via a conduit 108, connected to the inlet 104 at an upstreamend of the first intake air chamber 90, in the direction of air flow. Asshown in FIG. 5, the conduit 108 communicates with the second intake airchamber 106 through an outlet 110 of the second intake air chamber. Theconduit 108 is attached to the inlet 104 and the outlet 110 viacouplings such as band clamps 112.

[0073] As shown in FIG. 3, the second intake air chamber 106 includes aninlet 114, which is generally open to the engine compartment 42, so asto allow air from the engine compartment 42 to enter the second intakeair chamber. The second intake air chamber 106 preferably includes anL-shaped member 116 protruding from an end surface of the second intakeair box. The L-shaped member 116 is spaced from and opposed to the inlet114, so as to shield the opening from water that may inadvertentlysplash into the inlet 114 during the operation of the watercraft 10.

[0074] Constructed as such, the second intake air chamber 106, theconduit 108, and the first intake air chamber 90 define an induction airflow path for air entering the engine 50 for combustion purposes.Furthermore, by constructing the induction system 12 in the form of afirst chamber connected to a second chamber by a conduit, the inductionsystem 12 provides for the efficient use of the relatively small amountof space available in a small watercraft.

[0075] For example, as is illustrated in FIGS. 4-6, the enginecompartment 42 is nearly completely filled by the engine 50. As shown inFIGS. 4 and 6, the width of the engine 50 is nearly as wide as theengine compartment 42, along a direction transverse to the longitudinaldirection of the watercraft 10. Additionally, as shown in FIG. 5, theengine 50 is in close proximity to the fuel tank 30. Additionally,because the engine compartment 42 is positioned generally below the seatassembly 34, the maximum width of the engine compartment 42 is limited.For example, beacuse the passengers of the watercraft 10 sit directlyabove the engine 50, and on the seat assembly 34 in a straddle-typefashion, the width of the engine compartment 42 is limited to that whichis appropriate for a width of a straddle-type seat assembly such as theseat assembly 34. Therefore, by providing the induction system 12 with afirst intake air chamber 90 and a second intake air chamber 106, whichcommunicate with each other so as to define an induction air flow path,the present aspect of the invention allows the second intake air chamberto be arranged remotely from the first intake air chamber 90, thusefficiently using the space available within the engine compartment 42.

[0076] The second intake air chamber 106 is preferably mounted betweenthe engine 50 and the fuel tank 30, as shown in FIGS. 1 and 5. Arrangedas such, the induction system 12 utilizes a space which has heretoforegone unused within the hulls of known personal watercraft.

[0077] Additionally, the second intake air chamber 106 is preferablymounted directly to the engine 50. As shown in FIGS. 4 and 5, the secondintake air chamber 106 preferably includes a plurality of mountingbrackets 118 which are configured to receive bolts 120. As shown in thefigures, the bolts 120 connect the second intake air chamber to thefront portion of the engine 50. The bolts 120 may be threadably engagedwith a flywheel cover 122 of the engine 50 and/or mounting brackets 86,124, extending from the flywheel cover 122.

[0078] Mounted as such, the induction system 12 can be securely mountedto the engine 50 such that the engine 50, including the induction system12, can be assembled as a discrete unit, which may then be transportedto a distant facility for installation into a vehicle such as thewatercraft 10.

[0079] With reference to FIGS. 4 and 5, the induction system 12preferably defines an induction air flow path that contracts and expandsalong its length. For example, as shown in FIG. 5, the first intake airchamber 90 defines a cross-sectional air flow area 126 that is definedalong a plane generally perpendicular to the direction of air flow 128into the first intake air chamber 90. As shown in FIG. 4, the conduit108 defines a minimum cross-sectional flow area 128 which is smallerthan the cross-sectional flow area 126.

[0080] The second intake air chamber 106 defines a cross-sectional airflow area 130 defined along a plane generally perpendicular to the flowof air 132 through the second intake air chamber 106. Thecross-sectional air flow area 130 preferably is larger than thecross-sectional air flow area 128. The inlet 114 similarly defines across-sectional air flow area 134 that is smaller than thecross-sectional air flow area 130. While the cross-sectional flow areasof the first intake air chamber 90, the second intake air chamber 106,and the conduit 108 each have a generally uniform cross-sectional shapealong their respective lengths, each of these components can havevarying cross-sectional shapes in other applications.

[0081] In operation, a flow of air into the induction system 12contracts and expands as it flows therethrough. For example, as air fromthe engine compartment 42 enters the inlet 114, the air flow acceleratesas it passes through the cross-sectional air flow area 134. As the airflow moves past the cross-sectional air flow area 134 and through thecross-sectional air flow area 130, the air flow expands and thereforeslows. As such, the air flow is quieted and smoothed by the contractionand expansion. Similarly, as the air flow leaves the second intake airchamber 106 and enters the conduit 108, the air flow is contracted andtherefore accelerated, since the cross-sectional air flow area 128 ofthe conduit 108 is smaller than the cross-sectional air flow area 130.As the air flow exits the conduit 108 and enters the first intake airchamber 90, the cross-sectional air flow area of the air flow expandsgenerally to the size and shape of the cross-sectional air flow 126defined within the first intake air chamber 90. Accordingly, the airflow is again expanded, thereby slowing the air flow which quiets andsmoothes the air flow.

[0082] With reference to FIG. 7, the first intake air chamber 90 isshown with the cover member 98 removed and the inner wall 94 mounted tothe runners 96. As shown in FIGS. 8 and 11, the inner wall 94 includes aplurality of sleeves 136 in the form of annular intake ports defining aplurality of intake passages 138. As shown in FIG. 7, there is onesleeve 136 for each cylinder of the engine 50. As shown in FIG. 8, theintake passages 138 are generally aligned with the intake runners 96 soas to form individual air flow paths for each cylinder included in theengine 50.

[0083] As shown in FIGS. 7 and 8, the first intake air chamber 90 isprovided with at least one auxiliary air aperture 140 formed in one ofthe walls defining the first intake air chamber 90, so as to allow theinterior of the first intake air chamber 90 to communicate directly withthe surrounding atmospheric air in the engine compartment 42. As shownin FIG. 7, the first intake air chamber 90 preferably includes aplurality of auxiliary air apertures 140. At least one auxiliary airaperture 140 preferably is arranged between each pair of intake passages138. More preferably, a pair of auxiliary air apertures 140 is formedbetween each pair of intake passages 138.

[0084] As shown in FIG. 7, the auxiliary air apertures 140 arepreferably arranged above the intake passages 138, and are formed in theinner wall 94 of the first intake air chamber 90. The auxiliary airapertures 140 are arranged in the inner wall 94 so that the interior ofthe intake air chamber 90 communicates with a dead space 142 formedbetween the first intake air chamber 90 and the engine 50.

[0085] The dead space 142 is formed below a portion of the exhaustsystem 50 that is arranged above the fuel charge formers 102. The deadspace 142 is also between the engine 50 and the first intake air chamber90.

[0086] Positioned as such, the dead space 142 and the auxiliary airapertures 140 are substantially shielded from water that may collect inthe bottom of the hull section 16 and splash upon the engine 50. Asshown in FIG. 4, with the dead space 142 defined between the engine 50,the fuel charge formers 102, the first intake air chamber 90, and theexhaust system 50, the likelihood that water may splash into theauxiliary air apertures 140 is reduced.

[0087] With reference to FIG. 9, the inner wall 94 may include at leastone auxiliary air aperture 144 in addition or alternatively to theauxiliary air apertures 142. As shown in FIG. 9, at least one auxiliaryair aperture 144 is formed below the intake passages 138. Preferably, aplurality of the auxiliary air apertures 144 are formed below the intakepassages 138 so as to communicate the interior of the first intake airchamber 90 with the surrounding atmospheric air.

[0088] With the auxiliary air apertures 144 arranged below the intakepassages 138, the auxiliary air apertures 144 are arranged closer to alower surface of the lower hull section 16. Therefore, the auxiliary airapertures 144 allow the first intake air chamber to communicate with therelatively large supply of cooler air near the bottom of the lower hullsection 16.

[0089] It has been found that the total cross sectional air flow areadefined by the auxiliary air apertures 140 and/or 144 provided in theinner wall 94 should be from 5-25% of the point of maximum restrictionin the induction system, upstream from the first intake air chamber 90.In the illustrated embodiment, the point of maximum restriction islocated at the interface opening between the first air intake chamber 90and the conduit 108 (which in the illustrated embodiment is generallythe same as the cross sectional air flow area 128 of the conduit 108).Provided as such, the auxiliary air apertures 140, 144 allow anauxiliary flow of air to enter the first intake air chamber 101 when,for example, but without limitation, the throttle is suddenly moved froman idle position to the wide open position. As such, the inductionsystem retains quieting and smoothing characteristics associated withthe contraction and expansion created by the conduit and the first andsecond air intake air chambers. Preferably, the total cross sectionalair flow area defined by the auxiliary air apertures 140 and/or 144 isfrom about 10% to about 20% of the area 128.

[0090] In an exemplary embodiment, the diameter of the conduit 108 is91.6 mm, thereby creating a cross sectional flow area 128 of 6,586 mm².Four auxiliary air apertures (140 or 144), each having a diameter of 18mm, are provided in the inner wall 94, thereby forming a total of 1017mm², approximately 15% of the area 128.

[0091] With reference to FIG. 13, an outer face 146 of the inner wall 94includes a projection 148 arranged adjacent to each of the auxiliary airapertures 140. The projections 148 are preferably arranged above theauxiliary air apertures 140. With reference to FIG. 8, with theprojections 148 formed above the auxiliary air apertures 140, water thatmay splash onto or otherwise inadvertently drip along an upper edge ofthe first intake air chamber 90, is prevented from entering the interiorof the first intake air chamber 90.

[0092] Similarly, as shown in FIGS. 9 and 12, the outer face 146preferably includes a projection 150 formed adjacent to the auxiliaryair apertures 144. As shown in FIG. 12, the projection 150 is formedbelow the auxiliary air apertures 144. Arranged as such, the projections150 shield the auxiliary air apertures 144 from water that mayinadvertently splash onto the auxiliary air apertures 144, therebyreducing the amount of water that may inadvertently splash into thefirst intake air chamber 90.

[0093] As shown in FIG. 13, the outer face 146 preferably includes aplurality of ribs 152 projecting from the outer face 146. The ribs 152are preferably arranged so as to radiate from each intake passage 138 soas to stiffen the inner wall 94. Additionally, the outer face 146 mayinclude ribs 154 which are arranged between each pair of intake passages138 which also serve to stiffen the inner wall 94. Optionally, the innerwall 94 may also include a rib 151 extending from the outer face 146 andarranged along the outer periphery of the inner wail 94. The sleeves 136also preferably include ribs 155 formed on the ends of the sleeves 136which project from the outer face 146 of the inner wall 94.

[0094] As shown in FIG. 8, the first intake air chamber 90 is mounted toa flange 156 formed on the intake runner 96 such that each intakepassage 138 is aligned with each intake runner 96. The inner wall 94 issecured to the flange 156 via a plurality of bolts 158. Preferably, thenumber and size of bolts 158 is sufficient to support the weight of thefirst intake air chamber 90.

[0095] As shown in FIG. 9, the inner face 145 of the inner wall 94preferably includes a rib 159 surrounding the sleeves 136. The rib 159includes a plurality bolt mounting flanges 161 which extend over aportion of the sleeves 136 to provide mounting surfaces for the bolts158.

[0096] With reference to FIGS. 15-18, the cover member 98 preferably hasa rectangular shape corresponding to the shape of the inner wall 94. Asshown in FIGS. 15 and 16, the cover member 98 defines the inlet 104 ofthe first intake air chamber 90.

[0097] As shown in FIGS. 15 and 16, the inlet 104 is formed of anannular sleeve 160 which is configured to form a slip fit with theconduit 108. As shown in FIG. 15, the annular wall 160 is integratedwith the cover member 98 so as to form a transition portion 162 wherethe annular shape of sleeve 160 intersects with the generallyrectangular form of cover member 98.

[0098] The cover member 98 preferably includes a plurality ofreinforcing ribs 164 projecting from an inner face 168 of the covermember 98. As shown in FIG. 15, the ribs 164 are arranged in a grid-likepattern. Provided as such, the ribs 164 provide a stiffening effect forthe cover member 98, thereby inhibiting noise that may be generated byvibrations transferred to the first intake air chamber 90 from theengine 150, and/or induction air noise generated by the flow of air intothe induction system 12.

[0099] With reference to FIG. 8, the cover member 98 is sealably engagedwith the inner wall 94 via a joining portion 100. The joining portion100 is preferably comprised of a plurality of releasable couplings 172and a sealing device 174 disposed around the periphery of the firstintake air chamber 90.

[0100] With reference to FIGS. 8 and 13-15, each of the releasablecouplings 172 comprises a male portion 176 and a female portion 178. Themale portions 176 and the female portions 178 are configured to matesuch that a clasp member 180 is fittable over the outer contours of themale member 176 and the female member 178 when mated, as shown in FIG.8.

[0101] With reference to FIG. 13, the male portions 176 are comprised ofa projection 182 extending from a peripheral edge 184 of the inner wall94. The projections 182 include an arcuate portion 186. As shown in FIG.8, the arcuate portion 186 extends generally radially away from theperipheral edge 184 of the inner wall 94 and forms a generally U-shapedchannel 188 having an open end 190. The open end 190 faces a directiongenerally normal to the inner face 168 of the inner wall 98.

[0102] As shown in FIGS. 15 and 16, the female portion 178 includes aboss section 192 and a recess 194. The boss section 192 generallycorresponds in shape to the outer profile of the arcuate section 186.The recess portion 194 is configured to receive the male portion 176such that the arcuate portion 186 generally aligns with the boss section192. As shown in FIG. 8, when the male portion 176 is mated with thefemale portion 178, the C-shaped clasp 180 can be fitted over the maleand female portions so as to secure the male portion 176 in a matedposition with the female portion 178. Preferably, the outer contours ofthe male and female portions 176, 178 are configured so as to allow theclasp portion to be slid over one end thereof. As shown in FIG. 8, withthe clasp secured to the male and female portions 176, 178, the covermember 98 can be fixed to the inner wall 94.

[0103] With reference to FIG. 19, the sealing device 174 is comprised ofa rib 198 formed along the periphery of the cover member 98 and a groove196 formed along a corresponding periphery of the inner wall 94.However, the groove 196 could be formed on either the cover member 98 orthe inner wall 94 with the rib being formed on the other.

[0104] The sealing device 174 also includes a gasket 200. The gasket 200preferably includes a body 202 having a generally H-shaped cross sectiondefining a pair of substantially parallel walls 204. The parallel walls204 connected near a lower end 206 by a cross member portion 208 so asto form a gasket groove 210. Additionally, the gasket 200 preferablyincludes a pair of ribs 212 extending along a longitudinal length of thegasket 200. Preferably, the ribs 212, in a relaxed state, define a widthof the gasket 200 that is greater than the width of the groove 196.

[0105] Constructed as such, the gasket 200 is configured to provide asubstantially airtight seal between the cover member 98 and the innerwall 94 of the first intake air chamber 90. As shown in FIG. 21, whenthe gasket 200 is installed within the groove 196, the rib members 212deflect elastically so as to form a seal with the groove walls 196.Additionally, as shown in FIG. 21, with the rib 198 mated with thegasket groove 210, the space between the parallel walls 204 ismaintained so as to maintain the rib members 212 in contact with theinside walls of the groove 196. As such, the gasket 200 maintains asubstantially airtight seal between the cover member 98 and the innerwall 94 of the first intake air chamber 90.

[0106] As shown in FIG. 8, with the gasket 200 and the releasablecouplings 172 arranged as such around the periphery of the first intakeair chamber 90, the first intake air chamber forms a substantiallyairtight chamber which receives combustion air from inlet 104 and fromat least one of the auxiliary air apertures 140 and/or 144.

[0107] The at least one auxiliary air aperture 140 or 144 allows anauxiliary flow of air to enter the first intake air chamber 90 duringperiods of sudden acceleration. For example, when the engine 50 of thewatercraft 10 is idling, and the throttle is suddenly moved to a wideopen position, the flow of air into the engine 50 through the intakerunners 96 is rapidly increased. It has been found that intake airchambers of small watercraft tend to cause a transient delay orhesitation in the acceleration of the flow of air into the intake airchambers. This transient delay causes a delay before the engine canachieve an air flow rate required for the fuel air ratio needed formaximum engine output. Thus, acceleration of the watercraft has beendelayed by the time required for the air flow to accelerate to theproper rate.

[0108] By providing the first intake air chamber with at least oneauxiliary air aperture 140 and/or 144, however, an auxiliary flow of aircan enter the first intake air chamber 90 at the moment when thethrottle of the engine 50 is suddenly moved to a wide open position. Theengine 50 therefore can reach the fuel air ratio corresponding to themaximum power output of the engine more quickly than known watercraftengines.

[0109] As described above with reference to FIG. 7, the first intake airchamber 90 preferably includes a plurality of auxiliary air apertures140 and/or 144. At least one auxiliary air aperture 140 and/or 144preferably is arranged between each pair of intake runners 96. Arrangedas such, the auxiliary air apertures 140 and/or 144 provide auxiliaryflows of air that are evenly distributed between the intake runners 96.It has been found that two auxiliary air apertures 140 or 144 arearranged between each intake runner 96 is optimal.

[0110] Although this invention has been described in terms of a certainpreferred embodiment, other embodiments apparent to those of ordinaryskill in the art are also within the scope of this invention.Accordingly, the scope of the invention is intended to be defined onlyby the claims that follow.

What is claimed is:
 1. An engine induction system for a watercraftcomprised of a hull defining an engine compartment, an internalcombustion engine having a least one combustion chamber and beingsupported within the engine compartment, and a propulsion devicesupported by the hull and driven by the engine to propel the watercraft,the induction system comprising a first intake air chamber having aplurality of walls defining an interior volume and having an air inlet,the first intake air chamber communicating with the least one combustionchamber, a second intake air chamber having an air inlet and an airoutlet, the air inlet of the first intake air chamber communicating withthe air outlet of the second intake air chamber, and at least oneauxiliary air aperture formed in at least one of the plurality of walls.2. An engine induction system as set forth in claim 1 additionallycomprising a first cross sectional air flow area defined in theinduction system upstream from the first intake air chamber, the atleast one auxiliary air aperture defining a total cross sectional airflow area into the first intake air chamber that is from 5-25% of thefirst cross sectional air flow area.
 3. An engine induction system asset forth in claim 2, wherein the total cross sectional air flow area ofthe at least one auxiliary air aperture is from 10-20% of the firstcross sectional air flow area.
 4. An engine induction system as setforth in claim 3, wherein the total cross sectional air flow area of theat least one auxiliary air aperture is approximately 15% of the firstcross sectional air flow area.
 5. An engine induction system as setforth in claim 2 additionally comprising a conduit through which the airinlet of the first intake air chamber communicates with the air outletof the second intake air chamber, the conduit defining the first crosssectional air flow area at a minimum cross sectional passage formed inthe conduit.
 6. An engine induction system as set forth in claim 1,wherein the plurality of walls includes at least one inner wall formedbetween the interior of the first intake air chamber and the engine, theat least one auxiliary air aperture being formed in the inner wall. 7.An engine induction system as set forth in claim 6, wherein the at leastone auxiliary air aperture is arranged in an upper portion of the innerwall.
 8. An engine induction system as set forth in claim 6 additionallycomprising at least one induction port formed on the inner of wall, thefirst intake air chamber communicating with the at least one combustionchamber through the at least one induction port.
 9. An engine inductionsystem as set forth in claim 8, wherein the at least one induction portcomprises at least one pair of induction ports, the at least oneauxiliary air aperture being arranged between the induction ports ofeach pair of induction ports.
 10. An engine induction system as setforth in claim 9, wherein the at least one auxiliary air aperturecomprises at least a pair of auxiliary air apertures formed between eachpair of induction ports.
 11. An engine induction system as set forth inclaim 8, wherein the at least one auxiliary air aperture is formed on aportion of the wall above the induction port.
 12. An engine inductionsystem as set forth in claim 1, wherein the at least one auxiliary airaperture connects the first intake air chamber to a space formed betweenthe first intake air chamber and the engine.
 13. An induction system asset forth in claim 1 additionally comprising an exhaust conduitcommunicating with the least one combustion chamber and extending overthe first intake air chamber.
 14. An engine induction system as setforth in claim 13 additionally comprising at least one fuel chargeformer positioned between the induction port and the engine, the exhaustconduit extending above the at least one fuel charge former.
 15. Anengine induction system as set forth in claim 1 additionally comprisinga conduit through which the air inlet of the first intake air chambercommunicates with the air outlet of the second intake air chamber, thefirst intake air chamber defining a first cross-sectional flow area, andthe conduit defining a second cross-sectional flow area being smallerthan the first cross-sectional flow area.
 16. An engine induction systemaccording to claim 15, wherein the at least one auxiliary air aperturedefines a cross-sectional air flow area the smaller than the firstcross-sectional flow area.
 17. An engine induction system according toclaim 1 additionally comprising a projection formed adjacent the atleast one auxiliary air aperture and being configured to shield the atleast one auxiliary air aperture from splashing water.
 18. An engineinduction system for a watercraft comprised of a hull defining an enginecompartment, an internal combustion engine having a least one combustionchamber and being supported within the engine compartment, a propulsiondevice supported by the hull and driven by the engine to propel thewatercraft, and a fuel tank supported by the hull, the induction systemcomprising a first intake air chamber having a plurality of wallsdefining an interior volume and having an air inlet, the first intakeair chamber communicating with the least one combustion chamber, asecond intake air chamber having an air inlet and an air outlet, the airinlet of the first intake air chamber communicating with the air outletof the second intake air chamber, and means for allowing an auxiliaryflow of air to flow into the first intake air chamber.
 19. An engineinduction system according to claim 18 additionally comprising means forshielding the means for allowing from splashing water.
 20. An engineinduction system according to claim 18 additionally comprising at leastone projection formed adjacent the means for allowing, the projectionbeing configured to shield the means for allowing from splashing water.21. An engine induction system as set forth in claim 18, wherein theplurality of walls includes at least one inner wall formed between theinterior of the first intake air chamber and the engine, the means forallowing being formed in the inner wall.
 22. An engine induction systemas set forth in claim 21, wherein the means for allowing is arranged inan upper portion of the inner wall.
 23. An engine induction system asset forth in claim 21 additionally comprising at least one inductionport formed on the inner of wall, the first intake air chambercommunicating with the at least one combustion chamber through the atleast one induction port.
 24. An engine induction system as set forth inclaim 23, wherein the at least one induction port comprises at least onepair of induction ports, the means for allowing being arranged betweenthe induction ports of each pair of induction ports.
 25. An engineinduction system as set forth in claim 18 additionally comprising anexhaust conduit communicating with the least one combustion chamber andextending over the first intake air chamber, the means for allowingbeing positioned below the exhaust conduit.
 26. An engine inductionsystem as set forth in claim 25, wherein the plurality of walls includesat least one inner wall formed between the interior of the first intakeair chamber and the engine, the means for allowing being formed in theinner wall.